A. Background Information on Knee Braces
Knee braces are widely used to treat a variety of knee infirmities. Such braces may be configured to impart forces or leverage on the limbs surrounding the knee joint in order to relieve compressive forces within a portion of the knee joint, or to reduce the load on that portion of the knee. Moreover, in the event that knee ligaments are weak and infirm, a knee brace may stabilize, protect, support, or rehabilitate the knee.
The knee is acknowledged as one of the weakest joints in the body, and serves as the articulating joint between the thigh and calf muscle groups. The knee is held together primarily by small but powerful ligaments. Knee instability arising out of cartilage damage, ligament strain and other causes is relatively commonplace since the knee joint is subjected to significant loads during the course of almost any kind of physical activity requiring the use of the legs.
A healthy knee has an even distribution of pressure in both the medial and lateral compartments of the knee. It is normal for a person with a healthy knee to place a varus moment on the knee when standing so that the pressure between the medial and lateral compartments is uneven but still natural.
One type of knee infirmity that many individuals are prone to having is compartmental osteoarthritis. Compartmental osteoarthritis may arise when there is a persistent uneven distribution of pressure in one of the medial and lateral compartments of the knee. Compartmental osteoarthritis can be caused by injury, obesity, misalignment of the knee, or simply due to aging of the knee.
A major problem resulting from osteoarthritis of the knee is that the smooth cartilage lining the inside of the knee wears away. This leads to a narrowing of the joint space with the development of cysts and erosions in the bone ends. Because of the narrowing of the joint, bone comes directly in contact with bone, and an uneven distribution of pressure develops across the knee which may result in the formation of bone spurs around the joint. All of these changes ultimately lead to increasing pain and stiffness of the joint.
While there are no cures to osteoarthritis, there are many treatments. Individuals who have a diagnosis of isolated medial compartmental osteoarthritis of the knee are confronted with a variety of treatment options such as medications, surgery, and nonsurgical interventions. Nonsurgical interventions include the use of canes, lateral shoe wedges, and knee bracing.
Knee bracing is useful to provide compartment pain relief by reducing the load on the compartment through the application of an opposing external valgus or varus moment about the knee joint. Unloading knee braces have been shown to significantly reduce osteoarthritis knee pain while improving knee function.
B. Prior Art Knee Braces
There are many known unloading knee braces. An example of a known brace is described in U.S. Pat. No. 5,277,698 assigned to Generation II Orthotics, Inc. of British Columbia, which is incorporated herein by reference. Typically, braces of this type are designed to apply a moment about the knee through two mechanisms. The first mechanism is through the angulations of hinge components which induce a bending moment at a hinge. The second mechanism is provided by a three-point bending system via a force strap that spirals around the knee and applies a force to a prescribed aspect of the knee.
FIGS. 1 and 2 exemplify the application of forces by the brace on a leg and over a knee joint according to U.S. Pat. No. 5,277,698. The arrows B1 and B2 show lateral and force strap forces. The resulting moments in the leg due to lateral forces are shown by arrows Y1 and Y2. The principal force A is that applied immediately adjacent that compartment of the knee having osteoarthritis. FIG. 2 shows R as the normal axis of rotation of the knee. The resultant moment YR is a single rotational moment.
It has been found that as the force strap is increased in tension, the hinge valgus producing moment decreases. Therefore, the force strap and the hinge are found not to be adequately working in harmony. More specifically, it was discovered that the hinge produces about 20% of the total valgus moment in this brace. It is believed that since the hinge is aligned close to the knee, the strap urges the knee against the hinge. Moreover, the rigidity of this type of hinge limits the displacement of the hinge relative to the knee.
In a conventional brace having a hinge, a clearance is provided between the hinge and the knee to allow for movement of the knee towards the hinge. This results in a bulky brace since a large hinge is required which may extend at least an inch away from the knee.
It has been determined that if more unloading of the knee is required by the brace than is obtained from normal strap tension, and if the force strap is further tightened, the knee is drawn towards the hinge and might strike the hinge. This results in the hinge applying forces to the knee that counteract the force applied by the force strap. In turn, the additional tightening of the force strap is mitigated or negated by the force exerted onto the knee from the hinge.
For example, a study was conducted on a patient wearing a conventional knee brace having a force strap. In normal strap tension, the force strap component unloaded 5.8 Nm of the knee and the hinge unloaded about 2.2 Nm. By increasing the force strap tension, the unloading of the force strap resulted in 11.6 Nm, but the hinge resulted in unloading −2.4 Nm since the hinge was pressed against the knee.
As will be more fully evident in the ensuing discussion, the embodiments described herein are provided to overcome the deficiencies of prior art unloading braces by including arrangements that provide maximum unloading of the knee brace, while removing the mitigating effects of the hinges in known knee braces. Moreover, the embodiments of the invention are arranged for treating compartmental osteoarthritis, and have improved mechanical properties that remove undesirable rotational forces incurred by the brace and provide a more effective mechanism for generating a valgus or varus moment at the knee.
While known knee braces are successful at reducing pain at or stabilizing a knee joint, many users find these braces to be bulky, difficult to don, complicated to configure, and uncomfortable to wear. For these reasons, the embodiments described herein have streamlined features capable of providing relief for medial or lateral compartmental osteoarthritis, or functional stability of the knee without the attendant drawbacks of known unloading knee braces.